fixed issue 119

Author: horike37

lib/yamlParser.js

@@ -14,7 +14,7 @@ module.exports = {
     return this.serverless.yamlParser
       .parse(serverlessYmlPath)
       .then((serverlessFileParam) => {
-        this.serverless.variables.populateObject(serverlessFileParam).then((parsedObject) => {
+        return this.serverless.variables.populateObject(serverlessFileParam).then((parsedObject) => {
           this.serverless.service.stepFunctions = {};
           this.serverless.service.stepFunctions.stateMachines
               = parsedObject.stepFunctions